That's not an implication of that statement. I already explained why. I don't see a reason to just repeat myself.
The functional 'penalty' for hitting 0 is:
1. You start to take death saves when hit
2. You gain a level of exhaustion after the encounter
It really does represent my position. What it doesn't represent is your mischaracterization of my position.
That's not the only way for something to be a death spiral. If such a mechanic kicked in at half hp or 1/4 hp it would still be a death spiral mechanic. There's no reason the same doesn't apply to 0 hp.
I see no logically consistent reason it wouldn't be.
The logically consistent reason is why we have different degrees in a slope.
Not every hillside is a Cliff. And while you could certainly argue whether a 90 degree angle or greater is required for something to be a cliff, a 20 degree angle decline is not a cliff.
In a "Death at 0" situation you're walking on a perfectly flat grade toward a cliff about 100yds away, and then you just walk off the edge. (Death at -10 and Death at 3 failed saves is the same, you're just holding onto the edge of the cliff for a little while before you fall and someone could kick your hand or pull you up)
In yours, you're walking that perfectly flat grade toward the cliff, walking right off of it, and hovering in mid-air like Wile E. Coyote before either you scrabble back onto solid ground or look down and start falling.
In a Death Spiral situation (When every hit pushes you closer to that cliff) you're moving down a hill on a steadily increasing angle toward a cliff. Usually there's no way to back away from the cliff's edge, and everything you do after a certain point just brings you closer to the edge.
In an "Exhaustion when you've been downed" situation you're walking along a perfectly flat grade for about 100 yards toward the cliff. But you can either leap off (Failed saves) or take the stairs (Exhaustion) in order to walk farther toward or away from that cliff.
For a visual Illustration:
Walking off the cliff toward the camera would be Death at 0. You might grab on, you might not. Even if you do, you could still fall.
Walking off the cliff toward the left would be a Death Spiral. Even if you try to hold on, you're just gonna keep sliding.
Walking off the cliff toward the camera and landing on a lower rock formation would be Exhaustion on Defeat. You might be able to pull yourself up, but you're probably gonna fall further unless you focus on climbing up.